Generally, micro-structure fluid refers to fluid having a micro-structure, for example, a suspension in which solid particles are dispersed in liquid, an emulsion which is a mixture of two or more kinds of liquids, and a polymer solution. The micro-structure in fluid sensitively varies depending on shear stress applied to the fluid. Thus, when fluid flows, thermal transfer characteristics of the fluid are expected to be varied. Because the thermal transfer characteristics of the micro-structure fluid make it sensitive to temperature, when the thermal conductivity of the micro-structure fluid is measured, an environment for creating the steady-state temperature conditions is required.
Meanwhile, a hot-wire method which measures thermal conductivity under unsteady-state conditions is widely used because it can comparatively simply measure the thermal conductivity of a fluid or a solid in a short time. However, in the hot-wire method, the measurement is conducted in such a way that a probe is immersed into fluid. Hence, the hot-wire method is unsuited for the purpose of measuring the thermal conductivity of micro-structure fluid. For example, when thermal conductivity of a fluid, such as a suspension, an emulsion or a polymer solution, having a micro-structure is measured, heat is applied to the surroundings of the probe (hot wire) so that solid-phase concentration gradients are formed. The concentration gradients cause convection resulting from density difference. Thereby, the thermal conductivity cannot be accurately measured.